Method of forming cylindrical foamed cellulose rods enclosed in a rigid skin

ABSTRACT

A CYLINDRICAL ROD PARTICULARLY SUITABLE AS A CIGARETTE FILTER IS DESCRIBED WHICH IS COMPRISED PREDOMINANTLY OF FOAMED FIBROUS CELLOSE AND A WATER-INSOLUBLE POLYMER HAVING A GLASS TRANSITION TEMPERATURE OF AT MOST 50*C. AND A MINOR AMOUNT OF WETTING AGENT, THE WEIGHT RATIO OF THE POLYMER TO THE FIBROUS CELLULOSE BEING AT LEAST ABOUT 0.4, SAID ROD BEING ENCASED BY A SKIN OF SAID POLYMER.

United States Patent US. Cl. 264-47 5 Claims ABSTRACT OF THE DISCLOSURE A cylindrical rod particularly suitable as a cigarette filter is described which is comprised predominantly of foamed fibrous cellulose and a water-insoluble polymer having a glass transition temperature of at most 50 C. and a minor amount'of wetting agent, the weight ratio of the polymer to the fibrous cellulose being at least about 0.4, said rod being encased by a skin of said polymer.

This application is a divisional application of Ser. No. 562,095, filed July 1, 1966, and now Pat. No. 3,554,202. This invention relates to the preparation of stable cylindrical rods of foam cellulose encased by a rigid skin. More particularly, it is concerned with the manufacture of improved filters for cigarettes and improved tampons.

The cellulose foam filters described in application Ser.

No.- 444,-104filed Mar. 29, 1965, assigned to the assignee of the present application and now abandoned, have many advantages over prior art cigarette filters. However, one difiiculty with them has been their relatively poor firmness retention during the smoking of the attached cigarette. Tobacco smoke contains a significant amount of moisture such that a cigarette filter tends to lose its firmness during the course of smoking. Such a loss of firrrmess is of course objectionable to the filter cigarettesmoking .public. Moreover, previous methods of forming the requisite rod shape and dimensions have serious disadvantages from the point of view of time, cost and/ or the product quality. For example, in the aforesaid application, Ser. No. 444,104 the cellulose foam is drained and poured into molds and allowed to dry. Pouring into small tubes is a slow, tedious, costly process. The foam must be plugged, drained for a long period, dried, removed and compressed considerably. On the other hand, if the foam is cast in large sheets and dried and the filter rod is cut therefrom, some of the cellulose foam is wasted and more importantly, any rigid skin formed by the polymeric binder is lost. Furthermore, significant amounts of the polymeric binder drain off thus representing a loss of relatively expensive starting material.

It is an object of this invention to produce cigarette filter rods which will retain a high level of firmness during smoking. It is a further object of this invention to produce these filter rods in a simple and inexpensive manner.

It is a still further object to prepare improved tampons i.e. structures'introduced into a natural or artificial body cavity to arrest hemorrhage, absorb secretions or fill a defect. More particularly it is desired to prepare a tampon which can absorb up to about 15 times its weight of water and yet which at the same time can controllably exhibit a corresponding volume change of from zero to about times its original volume.

These objects have now been achieved by the process of this invention which broadly comprises forming a slurry of critical proportions of fibrous cellulose, wetting agent, and certain Water-insoluble resins in Water and expanding the slurry to a foam by agitation. The foam,

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without draining, is then extruded through a cylindrical tube and is deposited on a receiving surface in the form of wet, soft cylindrical units, and then dried.

The concentration of materials in the slurry is critical toward realizing the advantages of this invention. The wood pulp, or other cellulose fiber source, should constitute about 9 to 13 percent, the wetting agent about 0.2 to 2 percent, the water-insoluble resin about 5 to 10 percent and about 80 to 84 percent water. (All parts mentioned in this specification are by weight unless otherwise stated.) The weight ratio of water-insoluble resin to fibrous cellulose in the final product should be about 0.4 or greater.

The fibrous cellulose starting material is conveniently prepared from refined wood pulp having at least a moderate alpha cellulose content, i.e., at least about If the alpha cellulose content is too low, the Woody flavors of lignin are tasted by the smoker. Cotton linters represent anothergood source. The fiber length is advantageously less than /2 inch, and desirably less than inch. Longer fibers are more difficult to disperse but may be present in small amounts (e.g. about 1 to 10%) to add strength.

The water-insoluble resin should be one which has the ability to form a continuous film at relatively low temperatures upon the evaporation of water. The resin should have a glass transition temperature of 50 C. or less. Tables of glass transition temperature factors are readily available so that the glass transition temperature of copolymers based on the percent constituent monomers can readily be ascertained by adding the temperature factors of each constituent corresponding to its percentage in the copolymer. For example the glass (transition) temperature of a copolymer consisting of 55% methyl methacrylate, 40% ethyl acrylate and 5% butyl methacrylate can be calculated from the tables of Rohm & Haas Acrylic Glass Temperature Analyzer by adding together the corresponding temperature factors, 1.46, 1.59 and 0.17, respectively, to yield a net temperature factor of 3.22 which corresponds to a glass temperature of 38 C. The minimum film-forming temperature (M.F.T.) is slightly lower than the glass transition temperature due to the presence of impurities. Thus the glass transition temperature represents a readily ascertainable theoretical limit for determining whether a polymer or copolymer is within the scope of the invention.

Homopolymers or copolymers can be employed. Exemplary of suitable resins are polyvinylacetate, polyvinylidene chloride, polybutyl acrylate and cross-linkable acrylics. Homopolymers of vinylchloride, styrene and acrylonitrile are not suitable resins for this invention, however, copolymers in which these monomers are included and which have a suitable low glass transition temperature are utilizable. Numerous commercial formulations are available. It is necessary, of course, for end uses of the foam cellulose rods which involve significant contact with the human body, that the resin be physiologically harmless.

Polyvinyl acetate homopolymer is the preferred Waterinsoluble resin. The polyvinyl acetate advantageously is of high molecular weight, having an inherent viscosity (measured in standard manner using a 0.4% solution of the polymer in aqueous acetic acid at 25 C.) in the order of about 1.1-1.3.

It has been further discovered that the smoothness of the exterior surface of the drying filter rods critically depends on choice of Wetting agent. Non-ionic wetting for example cetyltrimethylammonium bromide. Still less preferred are the anionic wetting agents such as sodium lauryl sulfate and dodecylbenzene sodium sulfonate. When these latter wetting agents are used, the exterior of the rod has so many indentations that it cannot be effectively used as a commercial cigarette filter. The wetting Table I further illustrates the excellent results obtain: able employing the method of the instant invention. Filters prepared in accordance with the instant invention (Samples 1-6) are compared with filters prepared without observing the critical concentrations of this invention agent should of course be compatible with the other in- 5 (Samples 7 and 8) and filters prepared in accordancewith gredients and should have the property of forming rela- Example 3 of application Ser. No. 444,104 (Sample 9') tively stable bubbles or foam in their presence. and also commercial filters from a commercial cigarette The foam, produced in the conventional manner by brand (Sample 10). agitation, is transferred without provision for drainage to 10 In Sample 9 the PVAc/pulp ratio in the initial foam the extruding apparatus. It is then extruded through a cycomposition is significantly difierent from said ratio in lindrical tube and onto a wet surface in the form of a wet the dried product due to the loss of polyvinyl acetate cylindrical rod. This rod is surprisingly stable and is selfduring drainage. The two sets of values for sample .9 supporting and in contact with the foreign surface only correspond to two diiferent filter tips prepared from the tangentially at its bottom support. The wet rod is then dried foam. Firmness was again determined as the perdried in an oven to remove the water by evaporation. centage of the original diameter of the filter retained on Upon cooling, the water-insoluble resin concentrates to application of a one-pound load. The tip weight is ingive a firm structure with much of the resin wicking to cluded to show that the weight of the filter tips of this the surface to give a firm casing to the porous rod in the invention are comparable to those of present commercial form of a rigid skin. Any minor deviation of the rod from filter tips. 5

TABLE I Initial foam composition Filter tip firmness (weight percent) (percent) Pressure fIip Wetting PVAc/ Before Alter drop wt.

agent Water Pulp PVAc pulp smoking smoking mm. (H) (g.)

Sample 1... 0.5 83.5 10.5 5.5 .52 9s 83 32 0.135

Sample 2- 1 s2 11 6 .55 92 75 as 0.140

sam les 2 s0 12 s .50 89 7a 24 0.13%

Sample4 2 B3 10 5 .50 91 83 35 0.147

samgle 7--- 1 s1 13 5 .88 so 80 35 0.148 323E298-" 2 77 14 7 .50 92 71 29 0.147..

Wet- 0.3 93.6 3.3 2.8 .85 30 55 0.0a

Dry 1.5 ..'3 87 11.5 .10 s5 s1 45 70.10

Sample 10 so 73 65 0.14

circular cross-section can be readily corrected by rolling Note that although the ratio of polyvinyl acetate to between heated metal plates either about midway in the pulp in the extruded rods is much greater than in the rods drying period or after the drying. The rigid skin of this 40 prepared in accordance with the method of application filter rod leads to a high firmness retention. The process Ser. No. 444,104, said ratio is actually significantly less of this invention is illustrated in the following embodithan the initial ratio in the foam recipe in the latter ment. method.

EXAMPLE The stable foam cellulose rods of this invention can also be employed as tampons, i.e. inserted into body cavities,

The fOHPWmg mgredlent are Introduced mm a one They have a smooth exterior and are non-abrasive. Due quart Waring Blender: 20 grams acetate grade wood to the nature of the instant lnventlve process, the rod pulp, 30 grams polyvlnylacetate homopolymer emulsion 55% solids) 3 grams of saponin and 135 milliliters of meter 9 l Y i meXPenslvelY be adlut'led water meet varying size requirements merely by regulating the diameter of the extrusion cylinder. When swelling of the 31 g g gizg izg fi g z z i i rg tampon is not desired, the foamed cellulose rod as above t Wh n g flick slur Wa achieved the rate produced can be directly used. Where swelling of the. W3 e a S 1 W S tampon in situ is desired, as for example to afford a tighter of agitation was increased to produce a foam volume of fit the abovawmduced rod can be arsed in water 409' milliliters. The foam was then transferred to a cyhnsqueezed down and dried at up to about 17/10 to 1A of its drlcal chamber to which a pipe of 1 centimeter 1n dlamoriginal volume When thus ample ed the tam on eter, 1 inch long, is attached. The foam was forced d t a1 1 b P through this pipe by means of a plunger applied by O 1 S g g 3 g g 3 mer us varlan s e a ove escrl e oame ce 2?}: g i ig 3: 22: of i g z 32 2 2253; lulose rods and processes for their manufacture will be i gi g s l" z 9 C After a apparent to one skilled in the art within the scope of the p present invention. drying period of about 45 minutes, the rods were removed What is 01 ai m ed 6 ti :Oued f g z i i at 22 1. A method of preparing cylindrical foamed cellulose an a owe coo e m S e Wrappe rods enclosed in a rigid skin comprising (1 agitating a cigarette paper with the A usta-Betta Cigarette Roller and m o t b ht b0 t 9 137 fib u cut into two centimeter filter tips for attachment to cigamlx re c n ammg y w a u mus Ce lose, 5l0% of a water-insoluble resin havln a glass tranrettes. f

The firmness retention of these tips was determined by smon temperfimre 0 at most and t e a 1 1ty to smoking on a machine to a butt length of 3.() to 3.5 mi. foam a continuous film at relatively low temperatures meters in 9, two second g of 3 5 milliliters at one upon the evaporation of the mixture Di -2% of a wetting ute intervals. After smoking, the reduction in diameter agent selected from the group of non-101110 and whomof these tips under a one pound load was about 20%. 7o w t e a to p o a foam Commercial acetate filter tips are compressed about 20- (2) extruding sald foam, without prior drainage, through 25% under a similar test whereas the cellulose foam filter a cylindrical tube to form a wet cylindrical rod, (3) drying tips prepared as described in the aforesaid application the rod at a temperature of about IUD- C., and (4) Ser. No. 444,104 are compressed about 40% under such cooling said rod to form a firm structure due to wickin a t 75 of the resin to the surface of the structure.

2. A method according to Claim 1 wherein the wetting agent is non-ionic.

3. A method according to Claim 1 wherein the wetting agent is saponin.

4. A method according to Claim 1 wherein the waterinsoluble resin is vinyl acetate homopolymer.

5. A method according to Claim 1 wherein the rod is at least partially dried and rolled between heated plates.

References Cited UNITED STATES PATENTS 3,311,115 3/1967 Mueller et a1. 131-269 X 3,489,827 1/1970 Mueller et a1 264--50 OTHER REFERENCES Miller, M. L., The Structure of Polymers, New York, Reinhold, 1968, pp. 476-481 (SPE Polymer Science and Engineering Series).

PHILIP E. ANDERSON, Primary Examiner US. Cl. X.R. 

